This invention relates to flame retardant compounds which may be contacted with organic substances to reduce the tendency of the organic substance to flame. In particular, this invention relates to such flame retardants which act, at least in part, by their ability to intumesce.
For reasons of customer demand, government regulations, and product stewardship, those manufacturing and selling organic substances, particularly synthetic resins, have sought to reduce the tendency of those substances to flame. A suitable flame retardant additive must be economical to purchase, relatively nontoxic, easy to incorporate into the organic substance, nonmigrating, thermally stable, and effective at reducing the tendency of the substance to flame.
The use of flame retardants is not entirely satisfactory in some instances due to the tendency of many such compositions to be toxic, corrosive, or contributors to smoke formation.
One approach toward a workable flame retardant is that of intumescent flame retardants. Organic substances contacted with intumescent flame retardants behave generally as do organic substances contacted with other flame retardants, but upon contact with a flame, they soften, bubble, char, and swell, forming a thick, relatively non-flammable, thermally insulative barrier. Intumescent flame retardants are generally believed to require (a) a polyol component, (b) a dehydration catalyst (eg: phosphoric acid), and (c) a blowing agent. In some instances, a single molecule may provide two or even all three of the components. For instance, pentaerythritol phosphate may be regarded as providing a source of both the polyol component and the dehydration catalyst. In general, intumescent flame retardants are relatively non-toxic, non-corrosive, and low smoke contributors. However, they are also thermally unstable and tend to degrade at the temperature commonly encountered in polymer processing, resulting in discolorization of the polymer.
U.S. Pat. No. 4,454,064 (1984, Borg-Warner, Halpern) teaches the synthesis of pentaerythritol phosphate and its usefulness as an intermediate in the preparation of unnamed flame retardant materials. U.S. Pat. No. 4,341,694 (1982, Borg-Warner, Halpern) teaches the use of pentaerythritol phosphate as an intumescent flame retardant in polymers such as polyolefins. U.S. Pat. No. 3,808,296 (1974, Ciba-Geigy, Brunetti) discloses various hindered phenol esters of pentaerythritol phosphate and their use as "stabilizers" (ie: antioxidants), including such use with a multitude of coaditives including nitrogen-containing basic costabilizers such as melamine. U.S. Pat. No. 4,584,331 teaches the use of various esters and ether derivatives of pentaerythritol phosphate as (non-intumescent) flame retardants for a specific polyphenylene ether composition. U.S. Pat. No. 3,873,496 (1975, FMC, Hills) teaches the use of pentaerythritol phosphate as a non-intumescent flame retardant in polyester. GB 889,338 (1969, Hooker) teaches the synthesis and use of pentaerythritol phosphate as a stabilizer for vinyl halide resins.